1. Field of the Invention
The invention relates to humates and their use in printing ink and coating compositions. More particularly, the invention relates to the use of multivalent metal salts of humate compositions as components of printing and colorant coating compositions.
2. Brief Description of the Prior Art
A wide variety of organic and inorganic materials have been used over the centuries as components of printing and coating compositions.
For example, humic acids have been suggested as useful pigments in printing and compositure; see for example Steelink, Proceedings of the California Assoc. of Chemistry Teachers, Journal Chem. Ed. Vol. 40, No. 7, July 1963, pg. 379.
The term "humic acid" has been widely applied to acidic solids obtained from plant decompositions. More recently, humic acids have been regarded as the intermediate product or products which result in the conversion of lignin and other plant materials to hard coal. It is believed that in the decomposition of vegetable matter, the portion of the cell wall material consisting largely of lignin is converted into humus. In time, the humus may be converted progressively to peat, brown coal, bituminous coal and finally into anthracite. More usually, "humic substance" is applied as a generic term for the organic acids derived from humus or the top layer of the soil, containing organic decomposition products of vegetation and animal organisms in admixture with inorganic compounds, sand, minerals, metal hydroxide bases etc. The chemical structure of the humic acids has not been established, but they are believed to be large condensed ring, polymer-like molecules containing pendant carboxylic and phenolic groups. Depending on their solubilities, humic substances are usually classified as humic acid, fulvic acid, hymatomelanic acid or humin.
Monovalent alkali metal salts of humic acid or humate have also been described as useful components of printing inks; see for example U.S. Pat. No. 4,556,427.
We have discovered that multivalent metal humates used as binder components in aqueous ink compositions provide enhanced bleed resistance.